There are many radial piston pumps and motors, which have piston shoes and pistons associated thereto and where the piston shoes are guided inwards and outwards and mostly also endwards. Such devices work satisfactorily and reliably at certain sizes, pressures and revolutions. They are known for example from my U.S. Pat. Nos. 3,223,046; 3,270,685; 3,277,934; 3,304,883 and from many other patents.
Such radial piston pumps however, insofar as they had long piston strokes, had guide means for the piston shoes axially of the cylinders or of portions thereof, which resulted in relatively large axial dimensions of the device, so that the number of piston groups therein remained limited, because otherwise the fluid passages in the rotor would become too long for effective work. And further, those devices commonly had a rotary actuator means for the actuation of the piston stroke, which was revolvably mounted in bearings.
More recently, however, it is desired that radial piston pumps for example, operate with the rotary velocity of gas-turbines or of high speed revolving combustion engines. At those high rotary revolutions, however, the heretofore used guide means for the piston shoes are often unsatisfactory because the forward and backward acceleration forces on the piston shoes are becoming so high at such speeds, that the piston shoes tend to tilt a little in their guide means, which at very high speeds leads to welding between the guide faces of the piston shoes and of the guide means thereof. Also, the bearings for the actuator means are not able to revolve at such high revolutions, because their diameters are large in radial piston devices so that the velocity of the balls or rollers of the bearing would exceed their allowed maximum speed, if the pump runs at the speed of gas turbines or of high speed combustion engines. The bearings would then break.